The invention relates to the vibration isolation systems which employ nodal isolators. The nodal isolators develop opposing spring and inertia forces which produce a substantially zero vibratory motion of the isolated mass at predetermined frequencies of vibration or produce zero force feedback of an isolated mass to a non-isolated mass. In particular, the invention is utilized for isolating certain structural masses of helicopters or eliminating force feedback of certain structural masses of helicopters to the primary structure.
The vibrations which develop during the operation of a helicopter are not conducive to personnel comfort. In helicopters for military use, the problem is of less concern than in helicopters for commercial use, especially when the commercial use entails relatively long flight times. For example, it is the prime mission of Boeing's Model 234 helicopter to ferry personnel to and from off-shore drilling platforms. To accomplish this mission, airline passenger seats have been installed in the Model 234 helicopter. While this type of seat is helpful, it is not the entire answer since the seats must be anchored to the floor of the helicopter which, in turn, is anchored to the airframe which is subjected to the vibratory forces.
Because of the relatively long flight time, the Model 234 helicopter has been equipped with large fuel tanks. The fuel in these tanks represents a varying dynamic mass (changing fuel levels) which have a deleterious effect on airframe natural frequency placement.